Acids and Bases

Solvent Effects on Acid-Base Strength

Brian G. Cox

The first extensive, systematic coverage of acids and bases in non-aqueous solvents

Presentation and analysis of dissociation constants in different classes of non-aqueous media

Widespread correlations between dissociation constants and acid and solvent type

Quantitative aspects of acid-base chemistry

Practical details on the measurement of dissociation constants

Acids and Bases

Solvent Effects on Acid-Base Strength

Brian G. Cox

Description

Acids and bases are ubiquitous in chemistry. Our understanding of them, however, is dominated by their behaviour in water. Transfer to non-aqueous solvents leads to profound changes in acid-base strengths and to the rates and equilibria of many processes: for example, synthetic reactions involving acids, bases and nucleophiles; isolation of pharmaceutical actives through salt formation; formation of zwitter- ions in amino acids; and chromatographic separation of substrates. This book seeks to enhance our understanding of acids and bases by reviewing and analysing their behaviour in non-aqueous solvents. The behaviour is related where possible to that in water, but correlations and contrasts between solvents are also presented.

Fundamental background material is provided in the initial chapters: quantitative aspects of acid-base equilibria, including definitions and relationships between solution pH and species distribution; the influence of molecular structure on acid strengths; and acidity in aqueous solution. Solvent properties are reviewed, along with the magnitude of the interaction energies of solvent molecules with (especially) ions; the ability of solvents to participate in hydrogen bonding and to accept or donate electron pairs is seen to be crucial. Experimental methods for determining dissociation constants are described in detail.

In the remaining chapters, dissociation constants of a wide range of acids in three distinct classes of solvents are discussed: protic solvents, such as alcohols, which are strong hydrogen-bond donors; basic, polar aprotic solvents, such as dimethylformamide; and low-basicity and low polarity solvents, such as acetonitrile and tetrahydrofuran. Dissociation constants of individual acids vary over more than 20 orders of magnitude among the solvents, and there is a strong differentiation between the response of neutral and charged acids to solvent change. Ion-pairing and hydrogen-bonding equilibria, such as between phenol and phenoxide ions, play an increasingly important role as the solvent polarity decreases, and their influence on acid-base equilibria and salt formation is described.

Acids and Bases

Solvent Effects on Acid-Base Strength

Brian G. Cox

Author Information

Dr Brian G. Cox was educated at the University of Melbourne, followed by academic research or teaching posts at the Australian National University, the University of Stirling, Cornell University, and the Max-Planck Institut fur biophys. Chemie, Gottingen. He subsequently held industrial positions of Corporate Research Associate with ICI and Syngenta, and Associate Principal Scientist and Consultant with AstraZeneca. In addition, he has held Visiting Professorships at the Universities of Surrey, St Andrews, Bologna, and Chieti, and University College, Dublin, and most recently acted as Senior Advisor in Chemistry at the Institute of Chemical and Engineering Science in Singapore.

Acids and Bases

Solvent Effects on Acid-Base Strength

Brian G. Cox

Reviews and Awards

"Acid-base equilibria are one of the most important chemical reactions - affecting living systems through to industrial processes. This book covers everything any scientist would like to know about this topic from structural and solvent effects to the practical determination of dissociation constants. Cox follows his mentor R.P. Bell in presenting a lucid and well-written comprehensive text. Highly recommended." -- Michael Page, University of Huddersfield

"Acid-base equilibria are intimately coupled to many of the processes involved in synthetic and analytical chemistry, including reaction rates and selectivity, solubility and partition equilibria, catalytic cycles and chromatographic retention times. These equilibria are extraordinarily sensitive to the nature of the solvent, with some equilibrium constants changing by as much as 1010 on transfer from water to aprotic solvents. This book, by a practitioner with a lifetime's experience in the area, dissects a complex subject and provides a clear discussion of the several interacting factors that determine ionisation behaviour. It will be an invaluable resource to scientists involved with chemistry in non-aqueous solvents." -- John Atherton, University of Huddersfield